Exhaust heat boiler

ABSTRACT

The invention relates to an exhaust heat boiler used in conjunction with the furnaces for sintering or melting sulphide ores and concentrates. A characteristic feature of the boiler consists in making some of the evaporating and blowoff tubes of the evaporator platens from two coaxial tubes. Besides, the holes for the discharge of the cooled gas are arranged in at least one vertical row in the rear end wall of the boiler.

PTENTEDJUL"4 1972 3, 6 73 9 88 SHEET 10F 2 PATENTEDJUL 41972 l 3,673,988

SHEEVI 2 of' 2 EXHAUST HEAT BoILER The present invention relates to the exhaust heat boilers which utilize the heat of the gases exhausted from the furnaces for sintering and melting of sulphide ores and sulphide concentrates, particularly from the reverberatory air blast and hot-air blast copper-smelting furnaces as well as oxygen-enriched air blast furnaces flash-melting fumaces with hot-air blast, oxygen flash-melting furnaces, converters and from the fluidized-bed furnaces for sintering sulphide concentrates.

The claimed exhaust heat boiler can be used most successfully in all cases when it is necessary to cool aggressive gases heavily contaminated with the dust of the entrained charge, these gases, after cooling in the exhaust heat boiler being de rected for fine dust removal (e.g., in electrostatic precipitators) and then for the production of sulphuric acid.

Known in the art are exhaust heat boilers of the tunnel type which are provided with multistage positive circulation. These boilers incorporate a large radiant chamber lined with panel and roof cooling walls made of the tubes with multistage positive circulation. Located after the radiant chamber are longitudinal platens likewise made of the tubes with multistage positive circulation or of the steam superheater tubes. The longitudinal platens form corridors where moving gases are cooled. Under the radiant chamber and platens are located special bins for the dust precipitating from the gas ow and from the surface of the platens. Circulation of water through the tubes of the boiler cooling walls and platens is ensured by circulation pumps. These circulation pumps must be provided with steam and electric drives because stopping of the circulation pump even for a few minutes will result in the burning of the boiler tube surfaces; this creates certain difculties in operating the boiler. Besides, the circulation pumps draw considerable power which raises the operating expences of the boiler.

Considerable diculties encountered in the operation of the known exhaust boilers are caused by the variations of the gas temperature at the boiler` outlet, these variations resulting from the changes in the furnace load and in the degree of fouling of the heat surfaces with the entrained charge. The gases leaving the boiler enter the electrostatic precipitators at an excessively high or low temperature which reduces the efficiency of the precipitator and corrodes the equipment installed after the boiler.

An object of the invention resides in providing an exhaust heat boiler whose radiant and convection-radiant chambers would be so designed as to ensure long and continuous operation of the boiler with a minimum infiltration of air into the cooled furnace gases and a constant optimum temperature of said gases after the boiler.

This and other objects are accomplished by providing an exhaust heat boiler to be used with the furnaces for sintering or melting of sulphide ores and concentrates comprising consecutively arranged radiant chamber protected by wallmounted evaporator platens with natural circulation, constituted by the rows of evaporating tubes and a blowoff tube, built into the headers, and a convection-radiant chamber accommodating evaporator and air heating platens arranged parallel to the side walls and intended to cool the furnace gases, which generate the steam of the steam-and-water drum, superheat it in the superheater tubes and, being cooled, are discharged through the holes in the end wall of the boiler in which, according to the invention, some of the tubes of the evaporator platens are made of two coaxial tubes, of which the inner tube communicates with the water space of the waterand-steam drum installed above the boiler roof, the outer tube communicates with the steam space of the same drum and the blowoff tube of each evaporator platen is also made of two coaxial tubes, the rear end wall of the boiler being provided with at least one vertical row of holes for the discharge of cooled gases, each of said holes having an adjustable shutter.

In accordance with one of the embodiments of the invention the roof of the radiant chamber can be made of the steam superheater tubes with heat-insulating elements located above these tu bes.

The essence of the claimed invention consists in the followmg.

The natural circulation in the evaporator platens of the radiant and convection-radiant chambers of the boiler effected by means of coaxial tubes forms a natural ow circuit without the system of tubes supplying the feedwater and discharging the steam-and-water mixture, said tubes being usually arranged horizontally in the gas duct and causing said duct to be obstructed with the charge entrained by the gases.

Owing to the fact that blowoff is carried out through two coaxial tubes, water does not evaporate in the inner tube discharge through which are the slime and the salts of the evaporated water circulating in the platen tubes; evaporation does not take place because the inner tube is protected by the outer tube which ensures natural circulation of the evaporated water in the circular intertubular space. v

The above-described arrangement of the evaporator platens dispenses with the necessity for the row of holes in the boiler brickwork for the passage of the inlet and outlet tubes and headers which eliminates infiltration of air into the boiler furnace gases and preserves a high concentration of sulphur dioxide in the furnaces gases which is necessary for fine purication of the gases and their subsequent utilization.

The provision of holes in the rear end wall of the boiler, arranged in at least one vertical row, each of the holes being provided with an adjustable shutter, makes it possible to vary the discharge of the cooled gases from the boiler in height thereby cutting off a part of the boiler heat surfacesfrom the process of heat exchange, and maintaining a constant optimum temperature of gases after the boiler.

The roof of the radiant chamber made from the steam superheater tubes which ensure the necessary temperature of the wall without the use of circulation pumps and heat-insulating elements above them, increases the reliability and extends the life of said roof and excludes the necessity for costly refractory material which is usually employed for these purposes.

The invention is made more apparent by the accompanying drawings, in which:

FIG. l is a general view of the boiler according to the invention;

FIG. 2 is a front view ofthe avaporator platen of the boiler.

The exhaust heat boiler illustrated in the drawings consists of consecutively arranged radiant chamber 1 (FIG. 1) and convection-radiant chamber 2.

The side walls of the radiant chamber l are protected by wall-mounted evaporator platens 3 with natural circulation, while the roof is protected by the superheater tubes 4 covered on top by the heat-insulatin g elements 5.

The furnace gases are admitted into hole 6 in its front end wall 7.

Located inside the convection-radiant chamber 2, parallel to the side walls, are evaporator platens 8 and the air heater platens 9.

The rear end wall l0 of the boiler has two vertical rows of holes lll for the discharge of the cooled furnace gases; said holes are provided with adjustable shutters (not shown).

The lower brickwork of the boiler consists of a number of bins 12 for the removal of the charge entrained by the furnace gases.

The evaporator platens 3 and 8 are connected to the steamand-water drum 14 located above the boiler roof 13.

The evaporator platens 3 and 8 consist of tubes 15 and 16 (FIG. 2) which are welded into the headers 17 and 18.

Arranged coaxially inside the tubes 16 are tubes 19 whose upper ends are connected to the header 20 which is installed coaxially in the header 17.

The header 20 is communicated by the tubes 21 with the water space of the drum 14 while the header 17 is communicated by the tubes 22 with its steam space.

Connected to the lower header 18 are blowoff tubes made of two coaxial tubes 23 and 24.

The claimed exhaust heat boiler operates as follows.

The furnace gases are fed into the radiant chamber l of the boiler through the hole 6 (FIG. l

the boiler through a Flowing at a low velocity along the platens 3, the fumace gases are cooled and the entrained molten charge is hardened and precipitates partly into the bins l2.

After the radiant chamber 1, the gases flow into the convection-radiant chamber 2 and, moving at a low speed past the platens 8 and 9, are discharged through the holes l1.

The shutters of these holes control the amount of the discharged gases, thus ensuring a constant optimum temperature ofthe gases after the boiler.

The entrained charge precipitating from the gases moving past the platens 8 and 9 as well as the dust falling down from the external surface of the tubes of these platens are accumulated in the bins 12 and removed from them afterwards.

The steam generated by the boiler in the drum 14 is superheated in the superheater tubes 4 and supplied to the consumers.

The air is heated in the air heater platens 9 and also directed to the consumers.

The gases discharged from the boiler as well as the dust accumulated in the bins 12 are delivered for the ne removal of dust and subsequent technological utilization.

The invention can be realized as follows.

An exhaust heat boiler according to the Subject Matter wherein the roof of the radiant chamber is made of the steam superheater tubes protected on top by heat-insulating elements.

What is claimed is:

1. An exhaust heat boiler used in conjunction with the sintering or melting furnaces for sulphide ores and concentrates, comprising: a radiant chamber for the flow of furnace gases; wall-mounted evaporator platens with natural circulation, protecting said radiant chamber; rows of evaporating tubes of said evaporator platens, some of these tubes being made of two coaxial tubes; rows of evaporator platen blowoff tubes also consisting, each, of two coaxial tubes; headers with builtin said blowo and evaporating tubes; a convection-radiant chamber also intended for the flow of furnace gases and located after the radiant chamber; evaporator and air heating platens located in said convection-radiant chamber, parallel to its side walls; a roof of said radiant chamber; a steam-andwater drum installed above said roof, the water space of said drum communicating with the inner tube of the coaxial pair of evaporating tubes while its steam space communicates with the outer tube; steam superheater tubes wherein the furnace gases generate the steam of the steam-and-water drum; at least one vertical row of holes in the rear end wall of the boiler for the discharge of the cooled gas; and adjustable shutters of each of said holes.

2. An exhaust heat boiler according to claim l wherein the roof of the radiant chamber is made of the steam superheater tubes with heat-insulating elements above. 

1. An exhaust heat boiler used in conjunction with the sintering or melting furnaces for sulphide ores and concentrates, comprising: a radiant chamber for the flow of furnace gases; wall-mounted evaporator platens with natural circulation, protecting said radiant chamber; rows of evaporating tubes of said evaporator platens, some of these tubes being made of two coaxial tubes; rows of evaporator platen blowoff tubes also consisting, each, of two coaxial tubes; headers with built-in said blowoff and evaporating tubes; a convection-radiant chamber also intended for the flow of furnace gases and located after the radiant chamber; evaporator and air heating platens located in said convection-radiant chamber, parallel to its side walls; a roof of said radiant chamber; a steam-and-water drum installed above said roof, the water space of said drum communicating with the inner tube of the coaxial pair of evaporating tubes while its steam space communicates with the outer tube; steam superheater tubes wherein the furnace gases generate the steam of the steamand-water drum; at least one vertical row of holes in the rear end wall of the boiler for the discharge of the cooled gas; and adjustable shutters of each of said holes.
 2. An exhaust heat boiler according to claim 1 wherein the roof of the radiant chamber is made of the steam superheater tubes with heat-insulating elements above. 